Network Element For a Telecommunications Network Having Decoupled Control and Data Planes

ABSTRACT

A network element for a communications network having decoupled control and data planes may be in either a first state, the control plane and data plane are configured to interact, whereas, in the second state, the network element suppresses a control message for the data plane such that the configuration of the data plane is preserved. Accordingly, the network element may be in a second state when the data plane is undergoing maintenance such that there is no interaction between the control and data planes.

TECHNICAL FIELD

This invention relates to a network element for a telecommunicationsnetwork having decoupled control and data planes and a method ofoperating the same.

BACKGROUND

Telecommunication networks include a control plane and data plane.Conventionally, the functions of the control plane include systemconfiguration and routing (exchange of routing information). A routermay collect routing information from adjacent routers using routingprotocols, which is used to build a topology database (such as a linkstate database or routing table). The routing table is updatedinfrequently and is thus not suitable for fast packet forwarding.Accordingly, routers typically include a data (forwarding) plane toexpedite the forwarding process.

The data plane includes a forwarding table. The forwarding table ispopulated with data from the control plane allowing fast forwarding ofincoming packets at the data plane onto their destination. Aconventional architecture of a network element configured forimplementing both the control and data plane functionality is shown inFIG. 1.

In some networks (such as Generalized Multi-Protocol Label Switching,GMPLS, or Software Defined Networks, SDN), the control plane and dataplane are decoupled. The skilled person will understand that the term‘decoupled’ means that, ideally, a failure event in one plane does notaffect the other plane. Therefore, in the event of a control planefailure, the data plane may continue to forward traffic. It is alsopossible (but not mandatory) that the control plane and data plane areimplemented on separate physical paths and interfaces.

The network elements benefit from this decoupling as the data plane maycontinue to forward data traffic in the event of a fault in the controlplane. However, in the reverse situation (in which there is an event inthe data plane), the control plane in a conventional network continuesto be affected. The skilled person will understand that the term‘decoupled’ means that a failure in the control plane does not affectthe data plane.

As an example, in GMPLS controlled transport networks, it is common forthe network elements to undergo maintenance procedures such as asoftware download or internal database recovery. These operations do notdirectly affect the data plane (such as forwarding of existing datatraffic flows), but compromise the management plane and control planecapabilities of the network element as they may, for example, not beable to export consistent information to the Network Management Systemor react appropriately to possible failures.

Accordingly, network operators handle an event (such as a plannedmaintenance) in the data plane in several exemplary ways. In oneexample, the network operator disables the control plane whilst the dataplane is inactive. This downtime naturally results in the control planefunctions being unnecessarily lost for the time it is disabled. Inanother example, the control plane reacts to the data plane inactivityas if a failure event occurred in the data plane. This erroneousdetermination results in an unnecessary occupation of spare resourcesand, on reactivation, the data plane reverts to nominal path procedures.

It is therefore desirable to alleviate some or all of the aboveproblems.

SUMMARY

According to a first aspect of the invention, there is provided anetwork element for a communications network, the communications networkhaving a control plane and a data plane which are decoupled, the networkelement comprising a processor configured for implementing data planeand control plane functionality, wherein the network element isconfigured to be in one of: a first state in which a configuration ofthe data plane changes in response to the data plane receiving a controlmessage from the control plane, and a second state in which the networkelement is configured to suppress a control message for the data planesuch that the configuration of the data plane is preserved.

The present invention therefore defines two new states for the networkelement. These offer significant improvements in the management oftelecommunication networks having decoupled control and data planes(such as Generalized Multiprotocol Label Switching networks). Forexample, in the first state, the network element may operate as normal.However, in the situation in which there is an event in the data plane(such as programmed maintenance) then the network element may be in asecond state in which it is configured to suppress a control message forthe data plane such that the configuration of the data plane ispreserved. Accordingly, the network element may enter a state in whichan event in the data plane does not adversely affect the operation ofthe network element. In conventional network elements, an event in thedata plane would result in the control plane being disabled during theevent. However, in the present invention, the control plane may continueto receive and operate on routing information, but any control messagesmay be suppressed until the event is over and the network elementreturns to the first state.

This reduces the risk of unwanted recovery events (which occurred inconventional network elements after an event in the data plane).Furthermore, the network element may be provided with a memoryconfigured for storing the control message. Therefore, the control planemay continue to receive routing information, and store any controlmessages it creates in response in the memory whilst it is in the secondstate. The network element may subsequently act upon the stored controlmessages when the network element returns to the first state.

The present invention therefore decreases the operational expense of anetwork. That is, the stability of the telecommunications network isincreased as there is a lower risk of unnecessary restoration events,the control plane infrastructure remains active through the data planeevent, the status of the network element may be advertised to othernodes in the network, and pending operation on the control plane may notbe affected. Furthermore, service disruption is minimized as the controlplane may always be monitored by the Network Management System, there isno need for control plane reconfiguration or alignment, and restorationis always consistent.

When in the second state, the control plane may still receive routinginformation and prepare suitable control messages for the data plane.However, these control messages may be suppressed until the networkelement returns to the first state. Accordingly, circuit provisioning isstill possible even when there is an event in the data plane, as thecircuit provision is simply pending until the event is over.

The control message may be suppressed in a number of ways. For example,in the second state, the control plane may be configured such that itdoes not send the control message to the date plane. Alternatively, inthe second state, the control plane may be configured to send thecontrol message to the data plane and the configuration of the dataplane is preserved in response to the data plane receiving the controlmessage from the control plane (e.g. the data plane ignores the controlmessage).

In another example, in the second state, the data plane may beconfigured to reject the control message from the control plane.

The network element may further comprise a communication interfaceconfigured for sending a status message to a node in the communicationsnetwork, the status message indicating whether the network element is inthe first or second state. The status message may be sent to all nodesin the communications network. Therefore, other nodes in the network maybe informed of the state of the network element. In the case of circuitprovisioning, the external node may then determine to use a path whichdoes not include the network element when in the second state. Theexternal node may also be a Network Management System.

The data plane may be configured to send an event report to the controlplane when in the first state only.

In one example, the telecommunications network is configured forGeneralized Multi-Protocol Label Switching. However, the presentinvention would be suitable for any form of network having decoupledcontrol and data planes.

The network element may be configured for receiving an administratormessage (such as a configuration command) from a Network Operator of thetelecommunications network, wherein the administrator message mayconfigure the network element (1) to be in either the first or secondstate. The administrator message may be sent to the network elementsusing any suitable means, such as NMS, CLI, GUI, etc. Alternatively, thestate of the network element may be set internally.

According to a second aspect of the invention, there is provided anetwork element for a communications network, the communications networkhaving a control plane and a data plane which are decoupled, the networkelement comprising a processor configured for implementing data planefunctionality, wherein the data plane is configured to receive a controlmessage from the control plane and the network element is configured tobe in one of: a first state in which a configuration of the data planechanges in response to the data plane receiving the control message fromthe control plane, and a second state in which the configuration of thedata plane is preserved in response to the data plane receiving acontrol message from the control plane.

According to a third aspect of the invention, there is provided anetwork element for a communications network, the communications networkhaving a control plane and a data plane which are decoupled, the networkelement comprising a processor configured for implementing control planefunctionality, wherein the network element is configured to be in oneof: a first state in which the control plane is configured to send acontrol message to the data plane, and a second state in which thenetwork element is configured to suppress a control message for the dataplane.

According to a fourth aspect of the invention, there is provided amethod for controlling a network element of a communications network,the communications network having a control plane and a data plane whichare decoupled, the method comprising the steps of: if the networkelement is in a first state, the control plane and data plane areconfigured to interact; and if the network element is in a second state,the network element suppresses a control message for the data plane suchthat the configuration of the data plane is preserved.

A computer program product comprising computer executable code whichwhen executed on a computer may cause the computer to control a node toperform the method of the fourth aspect of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example,and with reference to the drawings in which:

FIG. 1 illustrates a network element of the prior art, showing themanagement, control and data planes;

FIG. 2 illustrates a network element according to a first embodiment ofthe invention;

FIG. 3 illustrates the network element of FIG. 2 in a first state,showing the management, control and data planes and memory;

FIG. 4 illustrates the network element of FIG. 2 in a second state,wherein a control message is stored in the memory;

FIG. 5 illustrates the network element of FIG. 2 in the first state,wherein the forwarding information base receives the stored controlmessage;

FIG. 6 illustrates a network element according to a second embodiment ofthe invention;

FIG. 7 illustrates a network element according to a third embodiment ofthe invention; and

FIG. 8 illustrates a method of an embodiment of the invention.

DETAILED DESCRIPTION

A network element 1 of a first embodiment of the invention will now bedescribed with reference to FIGS. 2 to 5. The network element 1 is partof a GMPLS telecommunications network having decoupled control and dataplanes. FIG. 2 illustrates the components of the network element 1,including a communications interface 9 a for sending and receivingrouting information and data packets, a memory 7 a (which will bedescribed in more detail below) and a processor 5 a. In this embodiment,the processor 5 a is configured for implementing the functions of boththe control plane and the data plane.

FIG. 3 is a schematic representation of the network element 1, showingthe various components in their respective planes. Accordingly, thenetwork element 1 is divided into the management plane, control plane 10and data plane 20. The control plane 10 includes an information base(implemented on processor 5 a). The data plane 20 includes a forwardinginformation base (also implemented on processor 5 a, but may also beimplemented on a separate processing module within the same networkelement 1) and a memory 7 a. The information base of the control plane10 is configured to send and receive routing information and theforwarding information base of the data plane 20 is configured to sendand receive data packets with external nodes (such as external nodes inthe telecommunications network, shown as external nodes in FIGS. 3 to 5)using the communications interface 9 a.

The network element 1 is configured to be in either a first maintenancestate or a second maintenance state. In the first maintenance state(indicated as ‘online’ in FIGS. 3 and 5), the control plane 10 isconfigured to send a control message 100 to the data plane 20 and thedata plane is configured to change its configuration in response to thecontrol message 100. Thus, in the first state, the control plane 10 anddata plane 20 interwork in a generally conventional manner.

The first state is shown in detail in FIG. 3, in which the informationbase sends a control message 100 to the forwarding information base. Theforwarding information base therefore updates its routing informationbased on the contents of the control message 100. This allows the dataplane to forward data packets to external nodes using the mostappropriate routing.

The network element 1 also includes a second maintenance state(indicated as ‘offline’ in FIG. 4). In the second state, the networkelement 1 is configured to suppress a control message 100 for the dataplane 20. The network element 1 may suppress the control message 100 ina number of ways. In one example, when the network element 1 is in thesecond state, it may suppress the control message 100 by preventing anyinteraction between the control plane 10 and data plane 20 such that thecontrol message 100 is not sent to the data plane 20. Accordingly, theconfiguration of the data plane 20 is preserved.

In another example, when the network element 1 is in the second state,the control plane 10 may send the control message 100 to the data plane20, but the network element suppresses the control message 100 by thedata plane 20 rejecting it. Again, the configuration of the data plane20 is preserved.

The network element 1 may therefore enter the second state (for example,during software download or internal database recovery), and the networkelement 1 then suppresses any control message during the maintenanceoperation. This ensures that the control plane 10 does not interact withthe data plane 20 during maintenance.

Furthermore, by keeping the control plane 10 operational (compared tothe disabled control planes of the conventional network elements duringmaintenance operations) means that it may continue to monitor itsconfiguration and resource availability (CIT, CC etc.), such that itdoes not lose configuration information (in the conventional networkelement, time was wasted when the control plane was subsequently enabledand reconfigured after the maintenance operation).

There are further benefits to keeping the control plane 10 operational.As noted above, the network element 1 further comprises a memory 7 a.When the network element 1 is in the second state, it may store acontrol message 100 for the data plane in the memory 7 a. In theexamples given above, the network element 1 may therefore suppress thecontrol message such that it is not sent to the data plane 20, butinstead the control message 100 is sent to the memory 7 a for storage.In the alternative example, the network element may suppress the controlmessage 100 by the data plane 20 rejecting it, and the network element 1then subsequently stores this rejected control message 100 in memory.FIG. 4 illustrates the control message 100 being sent to the memory 7 awhen the network element 1 is in the second state.

As shown in FIG. 5, the network element 1 may then send any storedcontrol messages 100 to the data plane 20 when it returns to the firststate (along with any further control messages 100 from the controlplane 10).

Thus, the network element 1 may store and subsequently react to controlmessages 100 that were intended for the data plane 20 when the networkelement 1 was in the first state, such that the configuration of thedata plane 20 is kept up to date. This has particular relevance in thecase of circuit provisioning, such that if the network element 1 is partof a new circuit but is in the second state when the circuit isprovisioned, it may store the appropriate control message 100 in memory7 a and the configuration of the data plane 20 is updated with the newcircuit once the network element 1 returns to the first state.

The network element 1 is also adapted such that its operational state isadvertised to external nodes (for example, the communication interface 9a may be configured to send a status message to an external node,wherein the status message indicates whether the network element is inthe first or second state). In this embodiment, the network element'soperational state is advertised to all nodes in the telecommunicationsnetwork. This ensures that the external nodes are aware of theoperational state of the network element 1, and therefore whether it isappropriate to use its resources. For example, if the network element 1is in the second state, an external node provisioning a new circuit maythen determine that the circuit should not include the network element1.

Furthermore, the status message may also indicate the state of thenetwork element 1 and if it has a memory for storing control messages.In this case, an external node provisioning a new circuit may thendetermine that the circuit may include the network element 1, but thecircuit will not be operational until the network element 1 returns tothe first state (when the network element 1 then configures the dataplane 20 according to the stored control message 100).

The network element 1 may therefore be relayed throughout thetelecommunications network using an appropriate protocol (e.g. OSPF).Additionally, the network element 1 may also send the status message toa Network Management System using management protocols.

A network element 2 of a second embodiment of the invention will now bedescribed with reference to FIG. 6. The network element 2 is again partof a GMPLS telecommunications network having decoupled control and dataplanes 10, 20. The network element 2 includes a communications interface9 b, a memory 5 b and a processor 7 b, which are all similar to thecomponents of the first embodiment. However, in this embodiment, theprocessor 7 b is configured to implement the data plane functionality(and not the control plane functionality). The control plane and dataplane 20 are therefore implemented on separate physical devices.

The network element 2 is configured to receive a control message 100from an external node implementing the control plane functionality(hereinafter, the “control node”). The network element, in this example,includes a forwarding information base (implemented on the processor 5b) which may then be updated (such as by reconfiguration of the dataplane to set up new data paths) in response to the control message 100.

The network element 2 is again configured to be in either a firstmaintenance state or a second maintenance state. In the first state, thenetwork element 2 is configured to change the configuration of the dataplane 20 in response to the control message 100. However, in the secondstate, the configuration of the data plane 20 is preserved in responseto the control message 100.

The network element 2 may preserve its configuration by ignoring thecontrol message 100 or by rejecting the control message 100 (e.g. byactively rejecting the control message 100 and sending a rejectionmessage to the control node). Upon returning to the first state, thenetwork element 2 may then react to any further control messages 100from the control node.

Alternatively, the network element 2 may store the control message 100in memory 7 b whilst the network element 2 is in the second state. Uponreturning to the first state, the network element 2 may then react toany stored control message 100 and any further control messages 100 fromthe control node.

As in the first embodiment, the network element 2 may advertise itsstate to external nodes (such as adjacent routers or a NetworkManagement System) by a status message. The status message may be sentto all nodes in the telecommunications network.

A network element 3 of a third embodiment of the invention will now bedescribed with reference to FIG. 7. The network element 3 is again partof a GMPLS telecommunications network having decoupled control and dataplanes 10, 20. The network element 3 includes a communications interface9 c, a memory 7 c and a processor 5 c. In this embodiment, the processor5 c is configured to implement the control plane functionality (and notthe data plane functionality). For example, the processor 5 c mayimplement an information base which may be updated by routinginformation received by the communications interface 9 c.

The network element 3 is configured to be in either a first maintenancestate or a second maintenance state. In the first state, the networkelement 3 is configured to send a control message 100 to an externalnode implementing the data plane (hereinafter, the “data node”). In thisexample, when the network element 3 receives routing informationindicating that a new route is to be provisioned on the data plane 20, acontrol message 100 is sent to the data node. The control message 100includes the relevant information for the data node to set up the newroute in the data plane.

In the second state, the network element 3 is configured to suppress thecontrol message 100. For example, the network element 3 may beconfigured to not send the control message 100 to the data plane 20(even though it has received routing information indicating that a newroute should be set up by on the data plane). The network element 3 mayalso be configured to store the control message 100 in the memory 7 cwhilst the network element 3 is in the second state. Accordingly, thecontrol message 100 is not sent to the data node, such that there is nointeraction between the network element 3 and the data node and theconfiguration of the data plane 20 is preserved.

As in the first and second embodiments, the network element 3 may beconfigured to advertise its state to an external node (such as anadjacent router or a Network Management System) by a status message. Thestatus message may be sent to all nodes in the telecommunicationsnetwork.

The skilled person will understand that the three embodiments of networkelements 1, 2, 3 of the present invention detailed above all alleviatethe problems of the interaction between the control plane and data planeof conventional networks whilst the data plane is undergoing maintenance(such as when downloading software or recovering the internal database).In conventional networks, the control plane is either disabled or ithandles the maintenance as if a failure occurred on the data plane(which has undesirable consequences such as unnecessary occupation ofspare resources and consequent back to nominal paths procedures). In theembodiments above, the network elements 1, 2, 3 may be in a second statesuch that the configuration of the data plane is preserved (for example,by the control plane suppressing a control message, or the data planeignoring or rejecting the control message). Thus, the control plane maycontinue to run without any interaction with the data plane, such thatthe circuits in place continue to carry traffic, control infrastructurecontinues to be operational, and the management plane continues tooperate on the network element, but there is no modification of the dataplane.

In the above embodiments, the telecommunications network implementsGeneralized Multiprotocol Label Switching. The introduction of thesecond maintenance state influences some of the GMPLS components. Thesewill now be discussed in more detail:

-   -   Protocols:        -   Link Management Protocol: a new administrative status may be            defined for the Label Switch Router, and the resource status            may be frozen. When a network element 1, 2, 3 is in the            second state, the ‘Hello’ message continues to flow. This            allows the control channels to remain operational.        -   Open Shortest Path First: the network element 1, 2, 3 state            (i.e. the first or second state) may be advertised in the            control plane domain. This may be achieved by adding a flag            to any of the sub-TLV included into the top level network            element TLV.        -   Resource Reservation Protocol: Path and reservation messages            may be processed and forwarded by the Label Switch Router            even when the network element 1, 2, 3 is in the second            state. The ‘Path’ and ‘Resv’ may be stored in memory 7 a, 7            b, 7 c whilst the network element 1, 2, 3 is in the second            state and may then be acted upon returning to the first            state. Notify messages may be processed and forwarded in            either state as they have no impact on the data plane 20.        -   Simple Network Management Protocol: A new Link Management            Protocol trap may be introduced (e.g. as a ‘status message)            and sent to the Network Management System to inform the NMS            of the change of state for the network element 1, 2, 3.    -   Path Computation Element:        -   During circuit restoration, network elements 1, 2, 3 in the            second state may be considered unavailable and all of their            resources may be considered busy.        -   During circuit setup, network elements 1, 2, 3 in the second            state may be considered available and their free resources            may be considered usable. The signalling procedure of such            circuits will succeed and the circuit will be activated as            soon as all of nodes in the circuit (including the network            elements 1, 2, 3) are in the first state.

In the first state, the networks elements 1, 2, 3 are configured suchthat the data plane 20 sends event reports to the control plane 10 andthe control plane 10 are configured to receive these event reports.However, the network elements 1, 2, 3 are also configured such that thedata plane 20 does not send an event report to the control plane 10 whenthe network elements 1, 2, 3 are in the second state.

A method for controlling a network element 1, 2, 3 of the presentinvention will now be described in more detail. The network element 1,2, 3 is part of a GMPLS telecommunications network having decoupledcontrol and data planes 10, 20. The network element 1, 2, 3 areconfigured to have a first and second maintenance state.

In the first state, the control plane 10 and data plane 20 areconfigured to interact. Thus, the control plane 10 and data plane 20continue to operate in a generally conventional manner. For example, ifthe network element 1 implements both the control plane 10 and dataplane 20, the network element is configured such that a control message100 is sent from the control plane 10 to the data plane 20, and the dataplane 20 is configured to react to the control message 100. In anotherexample, the network element 3 implements only the control planefunctionality and, in the first state, is configured to send a controlmessage 100 to an external node implementing the data planefunctionality. In another example, the network element 2 implements onlythe data plane functionality and, in the first state, is configured toreceive a control message 100 from an external node implementing thecontrol plane 10 functionality, and reacts to the control message 100(such as by modifying the configuration of the data plane 20).

In the second state, the network element 1, 2, 3 is configured tosuppress the control message 100 for the data plane 20 such that theconfiguration of the data plane 20 is preserved. For example, if thenetwork element 1 implements both the control plane 10 and data plane 20functionality, then the network element is configured to suppress thecontrol message 100 by either not sending the control message 100 to thedata plane 20, storing the control message 100 in memory 7 a, orensuring the data plane 20 does not react to the control message 100such as by the data plane 20 ignoring the control message 100 orrejecting it. Thus, the configuration of the data plane 20 is preserved.

In another example, the network element 3 implements the control planefunctionality only. In the second state, the network element 3 is eitherconfigured to suppress the control message 100 by either not sending thecontrol message 100 to the data plane 20, or by storing it in memory 7c. An external node implementing the data plane functionality thereforedoes not receive the control message 100 when the network element 3 isin the second state and the configuration of the data plane 20 ispreserved.

In another example, the network element 3 implements the data planefunctionality only. In the second state, the network element 3 isconfigured to either ignore or reject the control message 100 or storeit in memory 7 b. Accordingly, the configuration of the data plane 20 ispreserved.

FIG. 8 illustrates a flow diagram of an embodiment of the method of thepresent invention. In this embodiment, the network element 1 implementsboth the control plane and data plane functionality. The network elementis initially pending (step S1) before a control message 100 is initiated(step S2). In this example, the control message 100 is initiated inresponse to the network element 1 determining that the routinginformation of the forwarding information base is out-of-date and needsto be reconfigured (this may be in response to the network element 1receiving updated routing information).

In step S3, the network element 1 determines whether it is in the firstor second maintenance state. The state of the network element 1 isadministratively set by the network operator. If the network element 1determines that it is in the first state, the control message 100 issent to the data plane 20 (step S4) and the data plane 20 reacts to thecontrol message 100 (step S5). The configuration of the data plane 20 istherefore modified according to the contents of the control message 100,and the network element 1 returns to a pending state (step S1).

Alternatively, if the network element 1 determines that it is in thesecond state, the network element 1 suppresses the control message 100.In the embodiment illustrated in FIG. 8, the network element 1 storesthe control message 100 in memory 7 a (step S6). Accordingly, the dataplane 20 does not receive the control message 100 and its configurationis preserved.

In step S7, the network element 1 then determines whether it hasreturned to the first state (which will be administratively set by thenetwork operator). If the network element 1 remains in the second state,then the network element 1 continues to suppress the control message 100such that the configuration of the data plane 20 is preserved. However,once the network element 1 returns to the first state (i.e. it receivesa message from the Network Operator which reconfigures its maintenancestate), the data plane 20 receives the stored control message 100 (stepS8) and, in step S9, reacts to it in a conventional manner (e.g. bymodifying the configuration of the data plane 20).

In the above embodiments, the telecommunications network is configuredfor Generalized Multiprotocol Label Switching. However, the skilledperson will understand that the network elements 1, 2, 3 and the methodof the present invention are applicable to any type oftelecommunications network having decoupled control and data planes(such as Software Defined Networks).

The skilled person will also understand that it is not essential for thenetwork elements 1, 2, 3 to include a memory 7 a, 7 b, 7 c. However, byincluding a memory 7 a, 7 b, 7 c the network element 1, 2, 3 may store acontrol message 100 for the data plane 20 whilst the network element 1,2, 3 is in the second state, and subsequently react to the controlmessage (e.g. modify the configuration of the data plane 20) when itreturns to the first state. In FIGS. 3 to 5, the memory is illustratedas being part of the data plane 20, although it may also be consideredpart of the control plane 10. The skilled person will understand that inthe embodiment in which the control plane and data plane are implementedon the same device, the control and data planes may be implemented onthe same processor or using separate processing modules.

The skilled person will understand that any combination of features ispermissible within the scope of the invention, as claimed.

1-35. (canceled)
 36. A network element for a communications network, thecommunications network having a control plane and a data plane which aredecoupled, the network element comprising: a processor circuitconfigured to implement the data plane and the control planefunctionality; and wherein the network element is configured to be inone of: a first state in which a configuration of the data plane changesin response to the data plane receiving a control message from thecontrol plane; and a second state in which the network element isconfigured to suppress a control message for the data plane such thatthe configuration of the data plane is preserved.
 37. The networkelement as claimed in claim 36, wherein, in the second state, thecontrol plane does not send the control message to the date plane. 38.The network element as claimed in claim 36, wherein, in the secondstate, the control plane is configured to send the control message tothe data plane, and the configuration of the data plane is preserved inresponse to the data plane receiving the control message from thecontrol plane.
 39. The network element as claimed in claim 38, wherein,in the second state, the data plane is configured to reject the controlmessage from the control plane.
 40. The network element as claimed inclaim 36, further comprising a memory circuit configured to store thecontrol message.
 41. The network element as claimed in claim 36, furthercomprising a communication interface circuit configured to send a statusmessage to a node in the communications network, the status messageindicating whether the network element is in the first or second state.42. The network element as claimed in claim 41, wherein the node is aNetwork Management System.
 43. The network element as claimed in claim36, wherein the data plane is configured to send an event report to thecontrol plane when in the first state only.
 44. The network element asclaimed in claim 36, further configured to receive an administratormessage from a Network Operator of the telecommunications network,wherein the administrator message configures the network element to bein either the first or second state.
 45. A network element for acommunications network, the communications network having a controlplane and a data plane which are decoupled, the network elementcomprising: a processor circuit configured to implement data planefunctionality, wherein the data plane is configured to receive a controlmessage from the control plane; and wherein the network element isconfigured to be in one of: a first state in which a configuration ofthe data plane changes in response to the data plane receiving thecontrol message from the control plane, and a second state in which theconfiguration of the data plane is preserved in response to the dataplane receiving a control message from the control plane.
 46. Thenetwork element as claimed in claim 45, wherein, in the second state,the data plane is configured to reject the control message from thecontrol plane.
 47. The network element as claimed in claim 45, furthercomprising a communication interface circuit configured to send a statusmessage to a node in the communications network, the status messageindicating whether the network element is in the first or second state.48. The network element as claimed in claim 45, wherein the data planeis configured to send an event report to the control plane when in thefirst state only.
 49. A network element for a communications network,the communications network having a control plane and a data plane whichare decoupled, the network element comprising: a processor configured toimplement control plane functionality; and wherein the network elementis configured to be in one of: a first state in which the control planeis configured to send a control message to the data plane; and a secondstate in which the network element is configured to suppress a controlmessage for the data plane.
 50. The network element as claimed in claim49, wherein in the second state, the control plane does not send thecontrol message to the date plane.
 51. The network element as claimed inclaim 49, further comprising a communication interface circuitconfigured for sending a status message to a node in the communicationsnetwork, the status message indicating whether the network element is inthe first or second state.
 52. The network element as claimed in claim49, wherein the control plane is configured to receive an event reportfrom the data plane when in the first state only.
 53. A method forcontrolling a network element of a communications network, thecommunications network having a control plane and a data plane which aredecoupled, the method comprising: determining whether the networkelement is in a first state or a second state; if the network element isin a first state, configuring the control plane and the data plane tointeract; and if the network element is in a second state, suppressing acontrol message for the data plane such that the configuration of thedata plane is preserved.
 54. The method as claimed in claim 53, wherein,if the network element is in the second state, the method comprises thecontrol plane not sending the control message to the data plane.
 55. Themethod as claimed in claim 53, wherein in the second state, the methodfurther comprises: the control plane sending a control message to thedata plane, and the data plane receiving the control message and, inresponse, preserving the configuration of the data plane.